Asthma is a chronic respiratory disease, which is potentially life-threatening and an increasingly significant public health problem. In the United States 16.4 million non-institutionalized adults and 7.0 million children currently have asthma, accounting for 7.3% and 9.4% of these total populations respectively. Asthma involves multiple conditions and a major problem in fighting asthma is that its cause is unknown; however, there is a clear association of immune allergies in about 40% of asthmatics, and as the prevalence of allergies has increased, so has asthma. The hygiene hypothesis links the increasing allergic and autoimmune phenomena to excessively sanitary conditions early in life. Despite the appeal of this hypothesis, there are no clear examples of beneficial effects of microbial exposure. Our long-term goal is to understand the link between early microbe exposure and protection from allergic asthma. We will identify mechanisms involved in the shaping of the antibody repertoire by common environmental organisms, resulting in the induction and maintenance of non-allergen specific antibodies which block cellular mechanisms leading to sensitization by allergens expressed by bacteria, mold and fungi. Preliminary data shows that neonatal exposure to defined conserved bacterial antigens shared by a variety of allergen bearing organisms induce dramatic and permanent changes in the resulting B cell repertoire and that significant protection against airway sensitization is dependent on the timing of induction and the antigen targets of these antibodies. The two aims are to determine how early exposure to environmental antigens controls the development of B cells that make antibodies to microorganisms bearing allergens and then determine the mechanism of antibody- mediated protection against allergic airway disease. These outcomes will reveal new information on plasticity of the B cell repertoire and define developmental windows within which B cell clonal development can be manipulated to maximize levels of allergic airway-protective antibodies. Our long range goal underlying this approach is that an understanding of the immunological mechanisms involved in this protection will provide new therapeutic or vaccination options for treatment/prevention of allergic asthma.